How to build a climate model?

How is it that we go about building climate models?  One thing is, that we would like to build our model to represent everything that we know happens.  If we could actually do so -- mainly meaning if the computers were fast enough -- life would be simple.  As usual, life is not simple.

I'll take one feature as a poster child.  We know the laws of motion pretty well.  I could write them down pretty easily and with only a moderate amount more effort write a computer program to solve them.  These are the Navier-Stokes equations.  On one hand, they're surprisingly complex (from them comes dynamical chaos), but on the other, they're no problem -- we know how to write the computer programs to do conservation of momentum.  Ok entire books have been written on even a single portion of the problem.  Still, the books have already been written.

The problem is, if you want to run your climate model using what we know is a representation sufficient to capture everything we need to do, in order to represent everything we know is going on, you need to have your grid points only 1 millimeter apart.  That's ok, but it means something like 10^30 times as much computing power as the world's most powerful computer today. (A million trillion trillion times as much computing power.)

What do we do in the mean time?

Read more »

What is a model?

In the blogospheric talk about climate change 'model' gets mentioned a lot.  Sometimes it's merely descriptive, and often it is perjorative.  But it is mostly never really defined.  Like or loath them, nobody says just what models are.  Except for me, here and now.  (And probably a number of other people at other times and places -- but still, few and far between. :-)

'Obviously' a model is a particularly attractive human.  Right?  I've actually received email at my workplace (a 'modelling branch') from people who were trying to advance the careers of their models, in this sense of model.  We don't deal with that kind of model.

'Obviously' a model is to take the original (the Apollo Saturn V rocket that took people to the moon, for example) and duplicate everything about it, but at 1/32 the original size  Right?  Perhaps.  I know people tho like this sort of thing.  But again that's not what we mean either if we are discussing climate (or atmosphere, ocean, sea ice, land, glacier, ...) models.

For my purposes, a model is an idealized, and/or simplified, representation of the real world.  When we are interested in something as big and complex as climate, or even just the Arctic sea ice pack, we really can't cope with the whole thing in all of its glorious complexity.  We have to simplify the reality somehow.  That simplification is the model.

In this sense of 'model', models are everywhere.  We use a model for human behavior when we decide what somebody else means when they raise their hand in a certain way.  (is it open hand, or a fist?  did they just say 'hello', or 'I'm going to kill you'.  and so on)  Weather has also been modelled by using 'dishpans' -- Raymond Hide and David Fultz being two of the best examples of people taking this approach*.

Read more »

Bad philosophy 1

Different people are good at different things, which is no real surprise; but one of the common situations where some people suddenly become blind to this is scientists regarding philosophy.  Plus, well, most non-philosophers regarding philosophy.  I've had the good fortune to know a couple of serious philosophers of science, enough to appreciate that they've developed some understandings more profoundly than I have.  And, I'm immodest enough to extend that to 'more profoundly than most non-philosophers'.

One path of bad philosophy, the one which causes this post, follows from mistakes on the matter of certainty.  Or, naming it by way of the error it leads to, intellectual nihilism.  Certainty is a problematic concept for science, and science versus philosophy.  Errors come from both sides, so beware of throwing rocks.  From my philosophical vantage point, science is intrinsically uncertain.  My scientific excuse for that philosophical assumption is to consider the Uncertainty Principle.  It's enough for here to understand that you cannot, simultaneously, observe everything about a complex system (like an electron, an atom, or the climate system) exactly.  You can do pretty well, but there's always some uncertainty in the observations.

A different line of philosophy regards how and how well you can consider yourself to know something (epistomology).  One view of this derives from Karl Popper, under the label 'falsification'.  For here, it's enough to note that one can really only be confident about your knowledge to the extent to which you've tested it.  (Do, of course read further!)  Since you can only be confident about your knowledge to the degree to which you've tested the idea/hypothesis/theory/..., and any test of an idea (etc.) is intrinsically uncertain (uncertainty principle again), you can never be entirely certain that you have the right answer, idea, hypothesis, theory.  So some humility is in order -- for everybody.

Enter the bad philosophy.

Read more »

Multiple Working Hypotheses

In exploring Arctic ice minima I was not so much trying to reach conclusions as to find hypotheses for further testing and exploration.  Let's pick up the hypotheses side now, as I think it gets much too little attention in science education and science student practice.  In saying that, I'm projecting my bias, of course.

Part of that bias comes from having read and agreed with T. C. Chamberlin's Method of Multiple Hypotheses (1890).  Or at least liked my take on it.  It also has some correspondence to John Stuart Mill's ideas in On Liberty about a marketplace of ideas (1859), which I also liked.  The crux is, if we consider only one idea/hypothesis we are liable to be overly protective of it, or overly hostile to it.  Either way, we do not arrive at the best hypothesis for continued work.  Chances of us having started by selecting the best of all possible hypotheses, out of the infinity which could be generated, are essentially zero.

So, instead of starting with:

• Observe
• Make a hypothesis about those observations
• Make a prediction from that hypothesis
• Run an experiment to test the hypothesis

We try something more like:

• Observe
• Make multiple hypotheses that explain the observations
• Examine the hypotheses for how/where/when they lead to different predictions
• Run an experiment to distinguish between stronger and weaker hypotheses

A different take, or at least a different discussion, of the method of multiple working hypotheses is by L. Bruce Railsback

Read more »

Logical Fallacies and Scientific Method

Cracked had a very nice article on logical fallacies -- that we all make as a matter of course.  Also some good illustrations and suggestions.  Aside from the fact that it was a humor magazine that had such a nice article on rational thought, I was struck by the fact that each of the points mentioned are ones that the practice of science has addressed.

The 5 natural fallacies mentioned are:
5. We're Not Programmed to Seek "Truth," We're Programmed to "Win"
4. Our Brains Don't Understand Probability
3. We Think Everyone's Out to Get Us 
2. We're Hard-Wired to Have a Double Standard
1. Facts Don't Change Our Minds

Let's take a look at what science method does to combat these:

Read more »

Is it science?

One of the things I like to ponder is how to decide whether something is science or not.  An attempt to come up with a clear demarcation criterion is Karl Popper's, which gets more widely distributed as being "If it isn't falsifiable, it isn't science."   I'm not sure what he said himself, but philosophers tend to write books on these topics, rather than short sentences, so I'll guess that some details are lost in this version.

The question arises here because a recent question at the question place (yes, Robert, that's exactly what it's for) mentioned Popper.  I'll give a different response and discussion here.  (Same conclusion*).

For some cases, Popper's falsifiability criterion works well.  Religion is not science.  There is no observation, experiment, or test that will tell someone that their religion is wrong.  No matter what you observe, the religion can accommodate it.  Same thing for mathematics, actually, as it isn't necessarily concerned with observations.  Unfortunately, those (theology and mathematics) are the only two areas which can lay claim to absolute Truth (of a sort -- mathematical truth is only about mathematical things).  Science is left with only approximate truth -- the theory seems to work pretty well, the observations are pretty reliable.  But not absolutely reliable, and not absolutely perfectly.

For others, though, it's more difficult.  In the later 1800s, astronomers observed that the planet Mercury wasn't where it was supposed to be according to Newton's laws.  Its point of closest approach to the sun (perihelion) was moving by 43 seconds of arc per century too much$.  If Popper's criterion were correct, astronomers and physicists should have immediately thrown out Newton's laws and gone looking for something else.  Instead, some patches were suggested -- like a planet 'Vulcan', orbiting even closer to the Sun than Mercury, in just such a way to cause Mercury to behave as observed.  But it was never observed.  Eventually, Einstein proposed his theories of relativity to expand on Newton's laws.  Among other things, they explained why Mercury wasn't where Newton expected it to be.

For climatology, Popper is not so much relevant, or at least doesn't pose very much difficulty.

Read more »

If I were in charge?

Carrot eater asked me to consider what I would do if I were in charge of climate research.  I assume that he wasn't going for answers like 'find a different job promptly', which does make the question a little more theoretical.  Although I do have the copy of Nature that prompted his question, I've not read that article.  So these are my own thoughts.

My first thought is the least creative -- pretty much what is already being done in pretty much the proportions it is already being done.  No doubt that I would like to make some adjustments, say more for ice-related work.  But the main lines have gotten to be the main lines because they consistently show up as areas that deliver improvement to our understanding (satellites, paleoclimate) or they consistently show up as areas hampering our understanding (clouds).  Some areas probably get more funding than ideal, or less than ideal, because humans are involved and a particularly good, or bad, field leader can have effects beyond just writing good papers and proposals.

The two that I like for creative work should start as minor niches.  If my intuition is right, they'll grow markedly, at least for a time.  Because if my intuition is right, there's a lot to be learned from here that would be useful.  But it is pretty much just my intuition, so the starting investment shouldn't be huge.

The less exciting already has some work being done, at least in related fields.  Namely, 'no approximations' modeling.  We do know the equations that describe how fluids move, for instance.  We can write programs that carry out those equations accurately.  But once you're examining a volume of fluid larger than a moderately large fish tank (call it 50 gallons, 200 liters), you have to make approximations.  Computers can't deal with the full dynamics for a larger volume than that.  Nevertheless, in the 1950s and 1960s especially, quite a lot was learned about the general circulation of the atmosphere by doing 'dishpan' experiments.  Dishpans can be set back up, and the computers given accurate representations of them.  And then we can see how close the models come to the observations. 

More about the dishpans in a later post; they were a very clever way of approaching the atmosphere.  But here's a modern version's photo:
  and see also the original press release about the memorial lab, from which I got that picture.  I was among the last students Fultz fired up his working lab for.

The more exciting, to me, notion turns on an observation that I find very striking, and very few others in the field find at all interesting.  Makes it a high risk idea -- those other people are awfully smart, good chance they're seeing a flaw that I'm not.  I'll have a little explaining to do, but the short form of the observation is: for something like the global climate surface temperature field, you only need something like 12 numbers.

Read more »

Theory of Climate -- Philosophy

Is there a theory of climate, and if so, what is it?  That turns out to be a harder question than you might think.  It's my slight rephrase of a question asked in this month's question place.  The difficulty lies in the fact that 'theory' has several different meanings.

We can dismiss the most common daily life sort of usage -- a theory is something that is false.  It's used in comments like 'That may work in theory, but it doesn't work in practice.'  If we're talking about what happens in practice, we're talking about what happens in the real world.  Scientific theories have to apply to the real world.  If your idea makes false predictions about the real world, then the idea is (at least partly) false.  And, if your idea consistently makes false statements about the world, then it is not a theory, or even a hypothesis.  If there is a scientific theory of climate, it must be making true statements.

We can also dismiss the next most common daily life usage -- a theory is a WAG (wild guess).  A common sort of theory of this type is where I, for instance, theorize that since the last time I took my car to the shop, it got good service, that the next time I go, it will as well.  There's really very little data behind that thought, and very little analysis.  But it seems like a reasonable sort of statement.  Or the 'lucky socks' theory sports fans or athletes might have.  Their team won the last time they wore a particular pair of socks, so they theorize that the team will win again (or at least have a better chance of winning) if they wear the same socks for today's game.  Again, it seems reasonable to the person making the statement, but there's little data behind it and little analysis.

Now to consider the more difficult waters, where I hope that the two philosophers I know sometimes read will comment with appropriate corrections and elaborations.

Read more »